Work is in progress for the purification and chemical characterization of brain proteins. We emphasize the work on proteins that are either unique to the brain or relevant to special brain functions. In this respect, antigens specific to some neurons and axons are being purified and characterized chemically and immunologically. A brain protein that can promote the differentiation of glial cells are currently being purified. Various fractionation procedures have been tested and the best combination of these will be used for the final purification of the protein.